Toothpastes are generally of two types; opaque and transparent. Opaque toothpastes are generally white. They may also be coloured. Such toothpastes usually contain Calcium based abrasives; particularly chalk. Gel toothpastes usually contain abrasive silica. Multiphase toothpastes which have an opaque phase and a transparent phase are also known.
Toothpastes, particularly the chalk based ones, generally also contain thickening silica. It helps build viscosity. However, thickening silica, especially at higher levels, may adversely affect flavour delivery. This often compels formulators to dose an appropriate overage of flavour. Flavours are very expensive. Therefore even slight reduction in flavour can be economically significant. Therefore, it is desirable either to reduce the level of thickening silica, or preferably, have no thickening silica.
Toothpastes usually contain some polymers. Cellulosic polymers such as Sodium carboxymethyl cellulose (SCMC) are included as thickeners. Polymers of vinylmethyl ether and maleic acid, e.g. some polymers of the GANTREZ® family (GANTREZ® is registered trademark of International Specialty Products Inc (ISP)) are often used in toothpastes containing chalk. Known art indicates that such polymers are used for delivery of flavour.
One of the disadvantages of polymers of vinylmethyl ether and maleic acid, especially in toothpastes containing Calcium based abrasives is that unbalanced amount of such polymers can affect spreadability of the paste. Further, the paste becomes unstable after about a month of storage at elevated temperature. An arbitrary reduction in the level of such polymers cannot be a viable solution as it may adversely affects delivery of flavour.
Known art suggests using a combination of certain thickening polymers to solve some or all of the problems described earlier.
WO08041055 A1 (Procter & Gamble) discloses some examples of toothpaste compositions thickened with a material selected from xanthan gum, CMC, Gantrez® and carrageenan, albeit without explaining any technical effect of the combination of binders.
WO09134657 A1 (Procter & Gamble) describes toothpastes thickened with selected carrageenans, additionally having one or more of carboxyvinyl polymers, hydroxyethyl cellulose (HEC), natural and synthetic clays (e.g., VEEGUM® and LAPONITE®), CMC, SCMC, gum karaya, xanthan gum, gum arabic, gum tragacanth, colloidal magnesium aluminium silicate and finely divided silica. Disclosed toothpastes spread easily in the mouth. The toothpastes exhibit increased dispersibility in saliva during use, which provides for increased contact time of the composition with the user's teeth and oral cavity tissues such that the active dental agents are more rapidly available for beneficial activity.
WO2008068323 A1 (GLAXO GROUP LTD) discloses dentifrice compositions having a first thickening agent which is xanthan gum, a second thickening agent which is carrageenan and/or a polyacrylic acid and a third thickening agent which is thickening silica. Carrageenan and/or polyacrylic acid is said to reduce stringiness.
WO2007063507 A2 (Procter & Gamble) discloses dentifrice compositions containing a binder system made of:                (i) a hydrophilic clay material (e.g. LAPONITE®, CAB-O-SIL®)        (ii) a modified cellulose polymer, e.g., SCMC (such as BLANOSE® OPTICEL® 100, and AQUALON®), polyvinylpyrrolidone and HEC;        (iii) a carboxyvinyl polymer such as CARBOPOL® series and ULTREZ® 10; and,        (iv) a natural gum derived anionic polymer such as carrageenan, xanthan gum, gellan gum, and locust bean gum.        
The binder system swells or thickens in presence of polar solvent. Disclosed binder system provides good rheology at lower amounts of each binder, and thereby helps reduce costs.
EP0525913 A1 (Colgate-Palmolive, 1993) discloses viscoelastic toothpastes thickened with GANTREZ® type of polymers. Disclosed compositions have good stability against phase separation or syneresis, viscosity change in storage, and settling of dissolved, dispersed or suspended particles under high and low temperature conditions, freedom from fish eyes, texture and other cosmetic properties, ease of extrusion from a dispensing tube, pump or the like (easily shear thinned), good stand-up after extrusion (quick recovery of structure).
U.S. Pat. No. 5,192,529 A (Unilever, 1993) discloses a dentifrice composition thickened with carboxymethyl cellulose and hydroxylethyl cellulose in the range of 1:5 to 5:1. Disclosed compositions have low stringiness, good phase stability and proper texture.
We have determined that toothpastes having selective balance between a Calcium based abrasive, a copolymer of vinylmethylether and maleic acid and a clay have significantly better stability, even after being stored at elevated temperature. We have also determined that this also allows for complete removal of, or at least a significant reduction in thickening silica, with almost no adverse effect on rheology. In general, thickening silica is very commonly used in toothpastes.